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I have an existing Java application (Spring based) that currently does NOT have a web interface, nor does it run in a web container. It packages up nicely with a start program and just works.

What I need to do is add an administrative web interface for some administrative type things, retrieving real time metrics, and perhaps some graphs to give the users a warm fuzzy feeling knowing that everything is working. As we are a Spring shop, and some of our web applications already use Spring MVC it only makes sense to us, however, I'm not happy with the suggestions I've had from our internal Spring folks on how I should procede.

What would be the ideal way to bolt on this web interface?

  • Convert my application to a web application and have a web container launch the application. I not too keen on this approach is the web tier is really secondary to the primary application.
  • Create a separate project that packages as a war, embed Jetty in my existing app and have it load the war. I think I can use the context loader listener to make the root context of my application the parent to the web application spring context. This would involve breaking up my Maven project into 2 projects I believe. I can't use an existing web technology for communication between the web tier and the primary application as my primary application is not web enabled.
  • Embed Jetty and put the Spring MVC stuff directly in my app. While I've done this approach before, it does involve some ugliness - for instance exploding the JSP tag libs into my jar.

Any thoughts on some clean separation here?

Also of note, my current jar contains some utility applications which some shell scripts launch. Going a pure WAR route would make this not so easy, since I can't juse point java at my war file and choose a class to execute.

Thanks.

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If it's true that web is just a minor addition the application, migrating it to WAR and deploying in servlet container might be an overkill. Embedding web server/servlet container looks much simpler, although it doesn't have to be Jetty or Tomcat. You can use web server built into JDK or write one on top of or even raw sockets. But that's a hell to maintain.

Yet another solution to springs to mymind when reading:

web interface for some administrative type things, retrieving real time metrics, and perhaps some graphs

Maybe you don't need an interface, but monitoring infrastructure instead? Check out JMX (Spring has great support for JMX) - and write a second web application that simply connects to your standalone Java app via JMX and displays the metrics in fancy way. Another approach is to expose JMX via Jolokia, which translates JMX to REST services.

This approach has several advantages:

  • monitoring API is universal, and you get it for free

  • you don't have to use web client, monitoring application is completely decoupled,

  • finally changes to your original application are minimal. Check out this proof of concept: 1, 2.

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Very good point regarding JMX. I will research that further.
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It really depends on the structure of your existing Java/Spring app and how much of an API it provides. I've done something similar to this and I approached it by creating a separate Spring MVC project and then specified the existing Java app as a JAR dependency.

This is easy with Maven (or Ivy, etc) and provides nice decoupling. The trick is to be able to write service classes in the Spring MVC app which then access data via your dependent Spring app via a simple DAO class. That's why I stated at the beginning, that it depends on the structure of your original Java app. It has to be able to provide an API for data access that you can then plug your DAO (impl) into.

If this is not easily done, then the next option I'd suggest is simply converting your Spring app to a Spring MVC app. I've worked on another app where we did this. Using Maven, its possible to specify that the build can create either a war file or a jar file (or both). So it can be deployed as either a webapp (via war) or a normal app (via jar). Yes, the jar version has a bit of bloat but its a worthwhile compromise.

The question of embedding Jetty or using Tomcat via a war file is a completely separate issue that has its pros and cons. It shouldn't affect the approach you take in architecting the web app in the first place.

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I'm beginning to think I need to rethink the way I make Spring apps. Just go the webapp approach from the start.. Just in case I need to bolt on a web interface later.. Which is often the case, even if to provide a data extraction interface to our support guys.

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